text: In manufacturing, the simulated moving bed (SMB) process is a highly engineered process for implementing chromatographic separation.  It is used to separate one chemical compound or one class of chemical compounds from one or more other chemical compounds to provide significant quantities of the purified or enriched material at a lower cost than could be obtained using simple (batch) chromatography. It cannot provide any separation or purification that cannot be done by a simple column purification.  The process is rather complicated.  The single advantage which it brings to a chromatographic purification is that it allows the production of large quantities of highly purified material at a dramatically reduced cost.  The cost reductions come about as a result of: the use of a smaller amount of chromatographic separation media stationary phase, a continuous and high rate of production, and decreased solvent and energy requirements. This improved economic performance is brought about by a valve-and-column arrangement that is used to lengthen the stationary phase indefinitely and allow very high solute loadings to the process.
  In the conventional moving bed technique of production chromatography the feed entry and the analyte recovery are simultaneous and continuous, but because of practical difficulties with a continuously moving bed, the simulated moving bed technique was proposed. In the simulated moving bed technique instead of moving the bed, the feed inlet, the solvent or eluent inlet and the desired product exit and undesired product exit positions are moved continuously, giving the impression of a moving bed, with continuous flow of solid particles and continuous flow of liquid in the opposite direction of the solid particles.
  True moving bed chromatography (TMBC) is only a theoretical concept. Its simulation, SMBC, is achieved by the use of a multiplicity of columns in series and a complex valve arrangement, which provides for flow of the feed mixture and solvent, and "eluent" or "desorbent" feed at any column. The valving and piping arrangements and the predetermined control of these allow switching at regular intervals the sample entry in one direction, the solvent entry in the same direction but at a different location in the continuous loop, whilst changing the fast product and slow product takeoff positions to also move in the same direction, but at different relative locations within the loop.  
  Ref 3 explains that the advantage of the SMBC is high production rate, because a system could be near continuous, whilst its disadvantage is that it only performs one cut in mixtures. Thus, it is well-suited for separation of a binary mixture.  With multiple cuts, analogous to a series of distillation columns, multiple compounds can be separated from a mixture of more than two compounds.  With regard to efficiency it compares with the simple chromatography technique like continuous distillation does with batch distillation.